Seed Mass Distribution Research Articles

Ecological niche and phylogeny explain distribution of seed mass in the central European flora

Seed size is a crucial life‐history trait determining the amount of reserves that are available to establishing seedlings. The most frequently observed patterns in seed size distribution are a higher frequency of large‐seeded species in shaded habitats and a positive correlation of seed size with plant size. We analysed to what extent realised niche dimensions, as expressed by Ellenberg indicator values and plant functional traits such as plant height and life form, explained seed mass variation in the central European flora. By including information on phylogenetic relatedness of the species, not only contemporary ecology but also the evolutionary history of plant species could be taken into account. Seed mass evolution was slow and was best explained by selection‐inertia models with multiple adaptive peaks as a function of either habitat or life form. The highest seed mass optima were observed in the deciduous forest and saltwater and seashore habitats, and in phanerophytes in case of models with optima as a function of life form. The analyses showed that Ellenberg values were more important than habitat and life form in explaining seed mass distribution in the central European flora. The often observed relation between shade and large seeds was also evident in our study, but we found an equally important relation between large seeds and drought and a positive relation between seed mass and salinity. Our results indicate that not only plant size and competition for light but a complex set of factors influence the ecology of seed size, and that a more precise delineation of species’ niches improves the understanding of seed size evolution.

Do large-seeded herbs have a small range size? The seed mass-distribution range trade-off hypothesis.

We aimed to introduce and test the “seed mass–distribution range trade‐off” hypothesis, that is, that range size is negatively related to seed mass due to the generally better dispersal ability of smaller seeds. Studying the effects of environmental factors on the seed mass and range size of species, we also aimed to identify habitats where species may be at risk and need extra conservation effort to avoid local extinctions. We collected data for seed mass, global range size, and indicators for environmental factors of the habitat for 1,600 species of the Pannonian Ecoregion (Central Europe) from the literature. We tested the relationship between species’ seed mass, range size, and indicator values for soil moisture, light intensity, and nutrient supply. We found that seed mass is negatively correlated with range size; thus, a seed mass–distribution range trade‐off was validated based on the studied large species pool. We found increasing seed mass with decreasing light intensity and increasing nutrient availability, but decreasing seed mass with increasing soil moisture. Range size increased with increasing soil moisture and nutrient supply, but decreased with increasing light intensity. Our results supported the hypothesis that there is a trade‐off between seed mass and distribution range. We found that species of habitats characterized by low soil moisture and nutrient values but high light intensity values have small range size. This emphasizes that species of dry, infertile habitats, such as dry grasslands, could be more vulnerable to habitat fragmentation or degradation than species of wet and fertile habitats. The remarkably high number of species and the use of global distribution range in our study support our understanding of global biogeographic processes and patterns that are essential in defining conservation priorities.

Mixed pollen load and late‐acting self‐incompatibility flexibility in Adenocalymma peregrinum (Miers) L.G. Lohmann (Bignonieae: Bignoniaceae)

Mixed cross and self-pollen load on the stigma (mixed pollination) of species with late-acting self-incompatibility system (LSI) can lead to self-fertilized seed production. This "cryptic self-fertility" may allow selfed seedling development in species otherwise largely self-sterile. Our aims were to check if mixed pollinations would lead to fruit set in LSI Adenocalymma peregrinum, and test for evidence of early-acting inbreeding depression in putative selfed seeds from mixed pollinations. Experimental pollinations were carried out in a natural population. Fruit and seed set from self-, cross and mixed pollinations were analysed. Further germination tests were carried out for the seeds obtained from treatments. Our results confirm self-incompatibility, and fruit set from cross-pollinations was three-fold that from mixed pollinations. This low fruit set in mixed pollinations is most likely due to a greater number of self- than cross-fertilized ovules, which promotes LSI action and pistil abortion. Likewise, higher percentage of empty seeds in surviving fruits from mixed pollinations compared with cross-pollinations is probably due to ovule discounting caused by self-fertilization. Moreover, germinability of seeds with developed embryos was lower in fruits from mixed than from cross-pollinations, and the non-viable seeds from mixed pollinations showed one-third of the mass of those from cross-pollinations. The great number of empty seeds, lower germinability, lower mass of non-viable seeds, and higher variation in seed mass distribution in mixed pollinations, strongly suggests early-acing inbreeding depression in putative selfed seeds. In this sense, LSI and inbreeding depression acting together probably constrain self-fertilized seedling establishment in A.peregrinum.

Untangling interacting mechanisms of seed mass variation with elevation: insights from the comparison of inter-specific and intra-specific studies on eastern Tibetan angiosperm species

With increasing elevation, seed mass is expected to be either larger for its advantage during seedling establishment in stressful high-elevation environments ("stress-tolerance" mechanism) or smaller due to energy constraints. Based on the combination of inter- and intra-specific analyses on 4,023 populations of 320 Tibetan plant species, we found an overall positive within species but negative among species seed mass-elevation relationship, suggesting that regional seed mass distribution with elevation is affected mainly by the energy-constraint mechanism at among-species level, but by the stress-tolerance mechanism at within-species level. Moreover, both intra- and inter-specific analyses revealed a mass-dependent seed mass variation along elevation gradients: small seeds tended to increase but large seeds tended to decrease with increasing elevation, indicating that the stress-tolerance (respectively energy-constraint) mechanism may exert a stronger effect on elevational distribution of small-seeded (respectively large-seeded) populations or species. The mass-dependent seed mass variation along elevation gradients, however, was absent within woody and zoochorous species, implying substantial available resources and long time for seed development, and the covariation or coevolution between the mass of zoochorous seeds and their dispersers may allow for a (partial) decoupling of species' seed mass and their intra-specific variation with elevation. Together our results call for more comparative analyses at different taxonomic levels in detecting geographic variation in a trait.

Seed mass variation in common plant species in Wanfoshan Natural Reservation Region, Anhui, China

Aims Our objective was to investigate seed mass variation within species, genera and families, as well as its relationships with life form and plant phylogeny. Methods Seeds were collected at the Wanfoshan Natural Reservation Region from July to October 2011. Air-dried weight of 100 diaspores, including seeds and indehiscent and single-seeded fruit, was measured for each of three replicates. Seed mass variation and ecological significance were analyzed. Important findings Seed mass varied greatly from 10–3 g to 103 g. The seed mass distribution of various species was normal, as checked by the Kolmogorov-Smirnov Test. The mean weight of 1000 diaspores was 21.487 g. The seed mass of Momordica cochinchinensis (1775.192 g) and Aeginetia indica (0.006 g) were the heaviest and lightest, respectively. More than 60% of the species had a mean seed mass between 0.1 and 10.0 g. The seed mass of 105 species was 1.0 g. There were significant differences of seed mass among 68 families and eight life forms, as determined by one-way analysis of variance (p 0.001). Pearson’s relative analysis showed a negative relationship between seed mass and phylogeny (r = –0.079, p = 0.048) and a positive relationship between seed mass and life forms (r = 0.220, p 0.001). A significant difference was also detected at the generic level (p 0.001) in some families, including Compositae, Poaceae, Cyperaceae and Rosaceae.

Massive black holes lurking in Milky Way satellites

As massive black holes (MBHs) grow from lower-mass seeds, it is natural to expect that a leftover population of progenitor MBHs should also exist in the present universe. Dwarf galaxies undergo a quiet merger history, and as a result, we expect that dwarfs observed in the local Universe retain some `memory' of the original seed mass distribution. Consequently, the properties of MBHs in nearby dwarf galaxies may provide clean indicators of the efficiency of MBH formation. In order to examine the properties of MBHs in dwarf galaxies, we evolve different MBH populations within a Milky Way halo from high-redshift to today. We consider two plausible MBH formation mechanisms: `massive seeds' formed via gas-dynamical instabilities and a Population III remnant seed model. `Massive seeds' have larger masses than PopIII remnants, but form in rarer hosts. We dynamically evolve all halos merging with the central system, taking into consideration how the interaction modifies the satellites, stripping their outer mass layers. We compute different properties of the MBH population hosted in these satellites. We find that for the most part MBHs retain the original mass, thus providing a clear indication of what the properties of the seeds were. We derive the black hole occupation fraction (BHOF) of the satellite population at z=0. MBHs generated as `massive seeds' have large masses that would favour their identification, but their typical BHOF is always below 40 per cent and decreases to less than per cent for observed dwarf galaxy sizes. In contrast, Population III remnants have a higher BHOF, but their masses have not grown much since formation, inhibiting their detection.

The mass function of high-redshift seed black holes

Abstract In this Letter we derive the mass function of seed black holes that result from the central mass concentrated via disc accretion in collapsed haloes at redshift z ≈ 15. Using standard arguments including stability, we show that these pregalactic discs can assemble a significant mass concentration in the inner regions, providing fuel for the formation and initial growth of supermassive black holes. Assuming that these mass concentrations do result in central seed black holes, we determine the mass distribution of these seeds as a function of key halo properties. The seed mass distribution determined here turns out to be asymmetric and skewed to higher masses. Starting with these initial seeds, building up to 109 solar masses by z = 6 to power the bright quasars is not a problem in the standard Λ cold dark matter cosmogony. These seed black holes in gas-rich environments are likely to grow into the supermassive black holes at later times via mergers and accretion. Gas accretion on to these seeds at high redshift will produce miniquasars that likely play an important role in the reionization of the Universe. Some of these seed black holes, on the other hand, could be wandering in galaxy haloes as a consequence of frequent mergers, powering the off-nuclear ultra-luminous X-ray sources detected in nearby galaxies.

Altered weed reproduction and maternal effects under low-nitrogen fertility

The low-nitrogen status of highly weathered soils may offer a potential alternative for weed suppression in agricultural systems with N2-fixing crops. In this study, we used sicklepod as a model to evaluate weed response that might occur with managed reductions in nitrogen-soil fertility. A field study was conducted with the parental generation supplied 0, 112, 224, or 448 kg N ha−1. Decreased nitrogen fertility led to reduced shoot biomass, seed number, and total seed mass. Individual seed mass was lower, but seed % nitrogen was not affected. Analysis of seed-mass distribution confirmed that low parental fertility was associated with more small seeds as a proportion of total seeds produced. Additional experiments in hydroponics culture revealed slower growth rates of seedlings produced from small seeds when grown under low-nitrogen conditions. Competitiveness of plants from small (low nitrogen) and large (high nitrogen) seed classes was determined in a replacement-series experiment conducted in sand culture in a controlled environment at two densities and two levels of nitrogen nutrition. Plants produced from smaller seeds were less competitive in low-nitrogen fertility conditions, but plants from small and large seeds competed similarly when grown under high-nitrogen fertility. The results support the hypothesis that comprehensive management strategies to reduce nitrogen availability for weed growth in low-fertility conditions could decrease weed interference by decreasing growth and seed production of parental plants and through maternal effects that lower competitiveness of offspring.

Slope aspect affects the seed mass spectrum of grassland vegetation

Seed mass distribution in grassland communities of slopes of contrasting aspect was analysed in dolomite regions of the Pannonian Basin. Species frequencies were obtained for four pairs of data sets, which originated from corresponding south- and north-facing dolomite grasslands, thus forming four independent case studies. The data sets comprised 5–15 sample plots and 51–114 (average 85) species. The species were classified using an eight-class system reflecting their mean seed mass (MSM) records (class 1 being the lowest, MSM ≤ 0.2 mg; class 8 being the highest, MSM > 50 mg). Seed mass class distributions derived from slopes of contrasting aspect showed strong significant differences in chi-square tests for trend for all the four case studies. Small-seeded species (classes 1 and 2) showed a positive balance for the south-facing slopes, whereas large-seeded species (classes 5, 6, 7 and 8) were more frequent on north-facing slopes. Species with intermediate seed mass (classes 3 and 4) were not distinctive between the slopes. These results represent strong evidence of increased seed mass in the vegetation of north-facing grasslands, when compared to their south-facing counterparts. Among the phenomena potentially responsible for the new findings, we discuss the roles of microclimatic effects (especially drought stress and light regime), grass litter, interspecific competition and seed predation.

Experimental study and simulation of mass distribution of the covering layer of soybean seeds coated in a spouted bed

In previous work, it was observed that the covering of soybean seeds with bacteria and micronutrients enhances vigorous growth of the plant thereby avoiding use of ammoniacal fertilizers. In the spouted bed covering can be done by pulverization of the coater slurry on the soybean seeds using a pneumatic atomizer. The optimum thickness of the cover allows the fundamental gaseous interchanges for germination and provides the ideal conditions for bacterium activity. The objective of this work was to study the influence of the process variables on thickness of the cover. A simulation of the mass distribution of seeds was obtained using a population balance model. Through the results obtained the operational conditions under which the coating layer distribution were determined has the greatest uniformity.

Simple

A model predicting seedling emergence is described and applied to sugarbeet (Beta vulgaris L.). The input variables are the soil surface texture, soil temperature, rainfall, aggregate size distribution and position in the seedbed, sowing depths, characteristics of the seeds (initial seed mass distribution, germination time, and hypocotyl elongation distributions). A three‐dimensional seedbed layer is created where the aggregates and seeds are placed. Soil water content is assumed not to limit sugarbeet emergence (sowing conditions in northern Europe). The time needed to reach the soil surface is calculated using germination thermal time, soil temperature, the presence or absence of aggregates, and the hypocotyl elongation function. The ability of seedlings to break through the soil surface is a function of crust development and moisture. The seedling growth after emergence is calculated with reference to seed mass distribution, emergence delay, and the presence or absence of mechanical obstacles. The emergence prediction was tested in field experiments with four seedbeds, from fine earth to cloddy structure, and a sowing depth of 17 to 35 mm. The predicted number and sizes of clods encountered by seedlings and the calculated hypocotyl length were not significantly different from measured ones. Predicted germination times were longer than the observed ones (differences <5°C d); final rates were well predicted. Predicted vs. measured final emergence rates differed by less than 10%; changes with time differed from 15 to 30°C. This was due to the hypocotyl elongation functions, which must be improved. Further improvements will be to predict soil water content variations and effects on emergence via water stress and soil strengthening.

Comparisons of Methods to Compute Peanut Seed Size Distribution by Crop Growth Models

The value of a peanut crop is determined by yield and grade. The grade of peanuts is largely dependent on seed size distribution. Higher percentages of large seeds result in a higher grade and subsequently a higher profit for the grower. Peanut growth models currently predict yield and seed mass distribution, however, they do not predict seed size distribution which is critical for determining overall crop value. The objective of this work was to develop and evaluate a procedure to compute seed size distribution based upon the seed mass distribution predicted by a crop growth model. A linear relationship between individual seed mass and seed size was derived from field data and used to compute seed size distribution from predicted seed mass distribution. Mass of sound mature kernels (SMK) and extra large kernels (ELK) was predicted for 15 field experiments and compared to measured results. Three hypotheses were tested to improve the computed seed size distribution in the CROPGRO-Peanut crop growth model. Hypotheses relating to variable seed and shell growth rate reduced errors between predicted and observed mass of SMK and ELK. However, adjusting the average final weight per seed coefficient required by the crop growth model resulted in the best predictions of seed size distribution. The results of this work can provide a dynamic method of predicting mass of SMK and ELK required to determine crop grade, value, and harvest date when coupled with a dynamic crop growth model.